1. Field of the Invention
This invention relates generally to systems and method for control an optical pickup head for reading data from and writing data to data storage medium. More particularly, this invention is related to an improved method for optical disk tracking servo and focusing servo circuits enabled to compensate for non-continuous track segments or prolonged defect data tracks.
2. Description of the Prior Art
Conventional techniques of servo control and the compensation for errors that occurs during the processes of reading data from a data track are limited by an intrinsic assumption of these compensation algorithm that the servo control is relying on a normal track data-reading feedback to restore a normal operational mode. Without such a normal feedback signal, the whole servo control scheme fails and the data reading process stops. Conventional technologies of servo control implemented for controlling the pickup heads are therefore unable to deal with a data-recording medium that has a large defective area covering a length of the data recording tracks exceeding certain threshold length or discontinued data tracks where a pickup head is caused to wait indefinitely for the normal feedback signals before a normal servo control mechanism can function properly.
Specifically, optical discs are recording media for storing data, e.g., video and/or audio information, on their surfaces in the form of spirally track with pits and land information. The reproduction of recorded information on such optical discs is through an optical pickup. The optical pick-up shines a light ray, e.g., a laser beam, to track along the spiral-recording track and converts the reflected light into an electrical signal. A servo control mechanism is implemented to control the motion and positioning of the pickup head. The control mechanism is provided to control the objective lens or a mirror of the optical pickup device when moved by a stepping motor with lead screw or a linear motor to position the pickup head on the right track with precisely controlled focus on the data track to retrieve the data from a designated point on a designated data track.
FIG. 1 shows a typical conventional optical data storage and access system. An optical pickup head 102 projects a laser beam on a rotating optical media 101. An optical signal from the optical medium 102 is reflected and received by the optical pickup head (OPU) 102 that converts the reflected light from the optical media 101 into electrical signals. A radio frequency (RF) circuit 103 produces a tracking error (TE) signal and a focusing error (FE) signal to the respective tracking servo and focus servo processing circuits 104 and 105. Each servo circuit receives error signals and applies the gain control and phase compensator to feed the control voltage to stepper or linear motor driver 118 and OPU 102 actuator driver. The servo management process (SMP) 109 sets the servo gain and receiving control profile for tracking and focusing from the OPU 102 drivers, e.g., the focusing driver 113, the tracking driver 115, the spindle motor driver 116, the stepper/liner driver 118 and the spindle motor 117, for further processing. Referring to FIG. 1 again, the tracking servo circuit 104 receives the tracking error (TE) as a decoded signal for inputting to the SMP 109. The SMP 109 then generates servo control correction signals to the tracking driver 115. Similarly, the focus servo circuit 105 receives the focusing error (FE) as a decoded signal for inputting to the SMP 109. The SMP 109 then generates focus control correction signals to the focusing driver 113. The conventional servo control system as shown in FIG. 1 is not able to handle large area defects or data read/write operations for data stored in the discontinued data track segments due to the limitation that a convention servo control must use servo feedback or reflected optical laser beam data unavailable at these areas.
Typical tracking servomechanism control methods are the so-called 3-spot method, push-pull method and Differential Phase Detection (DPD) method. A tracking or focusing error is determined from the intensity of reflected light or the like position on an optical disc by a spot light ray from an optical pickup. There are different techniques disclosed by several prior art patents to manage and correct the errors during the data reading process. Emoto disclosed in U.S. Pat. No. 4,687,916 “Dual beams Optical pick-up device for both focus and error tracking detection”. In U.S. Pat. No. 4,703,468, Baba, et al. “Optical disc tracking servo circuit having compensation for disc defects and external disturbances” and U.S. Pat. No. 4,722,079, Matsumoto “Optical disk player capable of distinguishing external disturbances and local defects and adjusting servo gain accordingly” disclosed schemes to separate defects and external disturbance and servo corrections. In United States patent application 20010055247 Tateishi, Kiyoshi; et al. “Servo control apparatus for optical disc driver”. In a United States Patent Application Publication 20030223335 Chen, Chih-Yuan “Method of defect detection for optical disc drives”, and United States Patent Application 20030103425 Shidara, Kiyoshi “Optical disk apparatus” disclosed enhanced methods to improve the tracking servo control. In all cases, when the external disturbance is removed, the servo control circuit still expects to have the normal tracking feed back signals.
If the track defect is very long, see FIG. 3A, even with the defect mapping management method to map out the defect area to a different location, the available servo control methods can fail to keep or recover the optical pick-up to follow the prescribed track across the defect area and results a useless media. See FIG. 3, the track arrangement is non-continuously in track segments, the available servo control methods fails to keep the optical pick-up to follow the prescribed track across none available track area since no servo feedback signal is available.
Therefore, a need still exists to provide an improved data access device and CDROM, CDR, DVD and other data-card storage configurations that are compatible with the credit card size standard to process and store data therein such that more data can be available for card user authentication applications to overcome the above-mentioned difficulties and limitations.